1. Field of the Invention
The present invention relates to a structure of a crimping connection part of an aluminum electric wire and a metal terminal, and a method for manufacturing the same, specifically to a corrosion prevention technology of a crimping connection part.
2. Description of the Related Art
For the purpose of achieving weight reduction of vehicles such as automobiles, attention is paid to the use of an aluminum or aluminum alloy electric wire (hereinafter generically named “aluminum electric wire”). The aluminum electric wire is formed by applying insulating sheath to a single wire core wire or a core wire obtained by twisting a plurality of aluminum wires. In the case of wirings of vehicles such as automobiles, a wire harness prepared by bundling a plurality of electric wires formed by crimp-connecting a metal terminal on both ends of an aluminum electric wire and arranging the shape in conformity with a wiring route is used.
For the metal terminal, in general, a copper or copper alloy terminal (hereinafter generically named “copper terminal”) is used, and the aluminum electric wire is crimped by the copper terminal to obtain electrically connection. In that case, an open type wire barrel folded in a U-shape (core wire crimping part) is formed in a part of the copper terminal, the core wire formed by peeling off the insulating sheath of the end portion of the aluminum electric wire is located within the wire barrel, and the wire barrel is caulked to achieve crimping connection. In addition, an insulation barrel (insulating sheath crimping part) folded in a U-shape is formed on the end portion of the copper terminal, an insulating sheath of the end portion of the aluminum electric wire is located within the insulation barrel, and the insulation barrel is then caulked, thereby firmly crimping and holding the copper terminal on the aluminum electric wire (see, for example, JP-A-2010-108798, JP-A-2010-238393 and JP-A-2010-55901).
When moisture in the air is condensed and penetrates, or rainwater or the like penetrates into the crimping connection part between the aluminum electric wire and the copper terminal as thus crimp-connected, there is caused a problem of galvanic corrosion in which an ion of aluminum which is more easily oxidized elutes in correspondence to a difference of oxidation-reduction potential (ionization tendency) between the aluminum electric wire and the copper terminal as different metals from each other, thereby causing corrosion. Incidentally, in the case where a tin (Sn) plating is applied on the surface of the copper terminal, corrosion is similarly caused on the side of the aluminum electric wire due to a difference of oxidation-reduction potential between aluminum and tin. When the aluminum electric wire corrodes, there is caused such inconvenience that electrical characteristics of the connection part become instable due to an increase of contact resistance of the connection part, an increase of electrical resistance by a reduction of wire diameter, or the like.
Then, JP-A-2010-108798 proposes that a resin is coated on the entirety of the crimping connection part of the aluminum electric wire and the copper terminal, thereby preventing the penetration of water into the contact part of the aluminum electric wire and the copper terminal from occurring. In addition, JP-A-2010-238393 proposes that the crimping connection part of the aluminum electric wire and the copper terminal is covered by a metal housing body having a larger ionization tendency, namely a higher oxidation-reduction potential than that of aluminum and copper, and the metal housing body is sacrificially corroded, thereby suppressing the corrosion of aluminum. Furthermore, JP-A-2010-55901 proposes that a resin such as a silicone rubber is coated on an exposed core wire part from which the insulating sheath of the aluminum electric wire has been peeled off, to apply a waterproofing coating, the copper terminal is then crimped by a strong force to break the waterproofing coating, thereby bringing the aluminum electric wire and the copper terminal into contact with each other. According to this, the penetration of water into the contact part of the aluminum electric wire and the copper terminal is suppressed, whereby the corrosion of the aluminum core wire can be prevented from occurring.